Effects of rare earths on the microstructure, properties and fracture behavior of Mg–Al alloys

AZ91–xRE and Mg–6Al–xRE magnesium alloys were studied, where x is 0, 1, 2 and 3% (in weight percent, wt.%), respectively. Influence of rear earths (RE) on the microstructure was investigated. Fine morphology could be achieved by high cooling rate. By casting fluidity spiral specimens, fluidities of the alloys were achieved. The hardness and microhardness of the alloys was tested. RE improved fluidity and hardness. By casting specimens in permanent mold, tensile properties of the alloys with different RE additions at ambient and elevated temperatures were studied. RE had little effect on ambient temperature tensile strength of AZ91 alloy but greatly improved that of Mg–6Al alloy and high temperature tensile properties of both alloys. The fracture behavior of the alloys, which was changed by RE and high temperature, was examined by scanning electron microscopy (SEM) and optical microscopy. Fracture of the alloys is predominantly brittle cleavage or/and quasi-cleavage failure.